A heat pump (air-conditioner) generally includes a compressor, an outdoor heat exchanger, an indoor heat exchanger, a gas-liquid separator, an expansion valve, a four-way switch valve and the like. For example, JP Utility Model Publication (Kokai) No. 62-14280 proposes that in a heat pump including a plurality of heat exchangers, the plurality of heat exchangers are connected in series when the refrigerant is passed in one direction (normal direction), whereas when the refrigerant is passed in the other direction (reverse direction), the plurality of heat exchangers are connected in parallel, for the purpose of enhancing thermal efficiency and the like.
The above described four-way switch valve sets the refrigerant passing direction of the refrigerant cycle to be from the compressor to the outdoor heat exchanger, the expansion valve (pressure-reducing capillary tube), the indoor heat exchanger, and finally to the compressor in this order at the time of cooling, and sets the refrigerant passing direction to be from the compressor to the indoor heat exchanger, the expansion valve, the outdoor heat exchanger, and finally to the compressor in this order at the time of heating.